From p32, April 1999 issue of Scientific American, by Tim Beardsley. Regular print is from the original article. Italics are comments related to "The Degeneration of Man".
Humans have high mutation rates. But why worry?
All living things slowly accumulate mutations, changes in the string of chemical units in the famous DNA double helix that may in turn alter the form and function of a protein. A mutation that does affect a protein, if passed on to an offspring, might improve the progeny's chances in life or, more likely, harm them. Deleterious mutations, which can cause genetic diseases, are unfortunately more likely than beneficial ones, for the same reason that randomly retuning a string on the piano is likely to make the instrument sound worse, not better.
Under a benign environment, one that does not cull out subtle deleterious mutations by death, such mutations can accumulate in the species gene pool until the overall function of the organism reaches a level that is not survivable. For example, our modern civilization can support widespread individual degradation, to a point. A civilization can care for a number of defectives, but there is a limit, that when reached, results in the civilization itself collapsing. Suddenly the entire population, being required to revert to more primitive living conditions with now damaged capabilities, is unable to survive and the species becomes extinct.
Despite the hazard of harmful mutations, researchers until recently had only the vaguest notion of how often they occur in humans. Many mutations are thought to produce no obvious effect, yet they might still represent a subtle disadvantage to an organism carrying them. Adam Eyre-Walker of the University of Sussex and Peter D. Keightley of the University of Edinburgh recently examined the frequency of mutations in humans by studying how many have occurred in a sample of 46 genes during the six million years since the humans and chimpanzees last shared an ancestor. The results, published in 'Nature', were surprising: a minimum of 1.6 harmful mutations occurs per person per generation, and the number is more likely close to three. That number is high enough to pose a challenge to theorists.
Eyre-Walker and Keightley's approach was subtle. They first assessed how many human mutations occurred in the sample of genes that could not have produced any alteration in a protein and so must have been invisible to natural selection. (A fair proportion of mutations, even those occurring in active genes, do not cause any change in the protein that they encode.) They judged which differences in gene sequences between human and chimpanzees were caused by mutations in humans by comparing discrepant sequences with the equivalent gene in a third primate group. If the third group's sequence matched up with that of the chimpanzees, the change was surmised to have occurred in the human line.
From this number of "invisible" human mutations, Eyre-Walker and Keightley could calculate the theoretical number of mutations that should have resulted in altered proteins. The answer was 231. But only 143 such protein-changing human mutations were actually seen in the sample. The missing 88, they concluded, did occur at some point but were harmful enough to be eliminated by natural selection. That number leads to the estimate of perhaps three harmful mutations per person per generation.
There are about 80,000 genes in the human genome. To put these numbers in perspective: out of 400,000 protein altering mutations during that period, 150,000 were eliminated through death and suffering and 250,000 still reside in the human gene pool.
99.9% of the six million year period over which this study was made, was under a severe environment, not at all the civilized environment we now enjoy. The rate of accumulation of harmful mutations was extremely low during that time since the severe environment effectively eliminated them through death and suffering. When man invented agriculture and animal husbandry then later invented medicine and compassionate cultures (prisons instead of death for criminals, welfare and assistance programs, minimum wages, etc.), many serious genetic afflictions were subsidized and left in the gene pool to multiply and spread. All of those 250,000 deleterious mutations probably accumulated during the last 2,000 years. The rate of mutation has not changed, but the rate of assimilation into the gene pool is many orders of magnitude larger now than in most of the early times.
The proportion of mutations that is clearly harmful seems lower than most geneticists would have guessed. But the overall rate of human mutations is very high, and as a result of the rate of bad mutations is disturbingly high, too.
According to standard population genetics theory, the figure of three harmful mutations per person per generation implies that three people would have to die prematurely in each generation (or fail to reproduce) for each person who reproduced in order to eliminated the now absent deleterious mutations. Humans do not reproduce fast enough to support such a huge death toll. As James F. Crow of the University of Wisconsin asked rhetorically, in a commentary in 'Nature' on Eyre-Walker and Keightley's analysis: "Why aren't we extinct?"
Note that the rate discovered by these scientists is much larger than estimated in "The Degeneration of Man."
The reason we are not extinct is that ancient families were much larger. The childbearing period of a female is about 25 years and one child may be born each year. Families of 12 to 24 children were not unusual, even in early times in the US. Many tribes of primitives around the world still do. Child mortality was high, nature was merciless.
Crow's answer is that sex, which shuffles genes around, allows detrimental mutations to be eliminated in bunches. The new findings thus support the idea that sex evolved because individuals who (thanks to sex) inherit several bad mutations rid the gene pool of all of them at once, by failing to survive or reproduce.
Sheer nonsense. That sexual shuffling also spreads deleterious mutations far and wide, more than making up for any elimination through bunching. Sex was invented (a cruel invention by a cruel process) because it provided more opportunity for mutations and for more variations in combinations of traits. Although it resulted in far more deaths from genetic problems than in the prior cloning organisms, it also resulted in faster development if the species survived. Some did. The human is one of those. Now that we have modified our environment and it is no longer as effective in the removal of deleterious mutations, we are now degenerating mind, body and culture.
Yet natural selection has weakened in human populations with the advent of modern medicine, Crow notes. So he theorizes that harmful mutations may now be starting to accumulate at an even higher rate, with possibly worrisome consequences for health. Keightley is skeptical: he thinks that many mildly deleterious mutations have already become widespread in human populations through random events in evolution and that various adaptations, notably intelligence, have more than compensated. "I doubt that we'll have to pay a penalty as Crow seems to think," he remarks. "We've managed perfectly well up until now."
Keightley is correct in viewing human intelligence as a compensating device, but he does not realize that the degeneration from the accumulation of harmful mutations also affects the human mind, since its functioning is also subject to these same mutations. Under a benign environment, one that subsidizes harmful mutations, we are not only deepening in health problems, but our instincts and our intelligence are degenerating also.
It is extremely difficult for a professional biologist to consider the degeneration of the human. A basic tenet of the academic elitest ideology is diversity. Diversity is wonderful. All human beings are equal in value. These are ideological facts. To disagree is to be bigoted, perhaps racially, sexually , ethnically so, and is tantamount to academic suicide. If the degeneration of the human due to a crippled evolution process should ever be admitted to be true, then obviously genetic diversity would be undesirable, since it creates lesser humans. That concept would be intolerable to an ideologue.